The diverse microbial ecology in nature provides considerable variation in pathways of microbial degradation of hazardous wastes. This variation is not understood to the degree needed for design of biological remediation programs for contaminated environments (sites). An example of critical variations is the change in microbial populations and metabolism with change in environmental redox conditions. Some species thrive in very limited environments, such as methanogens, who can not tolerate the presence of molecular oxygen and generally are out competed by many other anaerobic species. Different species are capable of mediating different and some similar natural chemical and biological reactions. Although research examining these natural reactions has been proceeding for several decades, little is known about the response of microorganisms to the relatively recent anthropogenic compounds. This proposal addresses this issue. The two major goals of the proposed research are 1) to increase understanding of the possible degradation pathways of solvents in environments conducive to actual implementation, such as denitrifying and methanogenic, and 2) to develop microbial systems that exhibit enhanced degradative ability. In order to achieve the first goal, two related projects will examine the ecology of denitrifiers and methanogens as it relates to the degradation of solvents. Denitrifiers are capable of degrading compounds such as benzene and carbon tetrachloride. However, little is known about the mechanism; information which is critical to the application of denitrifiers to solving hazardous waste problems, Methanogens also have the capability to dechlorinate halogenated solvents. Knowledge about the mechanism of dechlorination, its dependence on primary substrate and on organism species is required for understanding the fats of these compounds in the environment and for designing remediation schemes. The second goal will be achieved when development of bacterial strains capable of complete destruction of pollutants are available and able to thrive in engineered systems. One project proposed here will attempt to include genetic material which defines solvent degradative ability in a particular microorganism (Pseudomonas sp. PK01). Sources of genetic material include the denitrifiers and methanogens described in the previous projects. The enhanced bacteria developed will be tested in laboratory-scale engineered systems for its ability and to measure its degradation rate.